There are several known methods of removing the iron content from ferrotitaniferous material. Most of these involve a reduction step to convert the iron content to a state whereby it may be conveniently separated from the relict titanium oxide material. For example in Australian Patent Specification No. 247 110 there is disclosed a multistep process for the upgrading of ilmenite wherein the ilmenite is reduced so that its iron content is metallized; the thus formed metallic iron is leached away from the titanium oxide material by a `rusting` process using an aqueous reagent. In another process described in U.S. Pat. No. 3,252,787 ilmenite is metallized and the iron content then removed by treatment with ferric chloride solution. In yet another process described in Australian Patent Specification No. 515 061 metallized ilmenite particles are subjected to a segregation treatment whereby small iron metal particles dispersed throughout each particle of metallized ilmenite are translocated and agglomerated to form large particles outside the relict particles.
For such processes which require removal of iron by means of reactions with liquids or gases it is desirable to have the metallic iron particles in a very fine state, homogeneously dispersed and accessible to the reactants through pores from the outside of the particles of metallized ferrotitaniferous material.
Studies on the reduction of ilmenite reported by G. Ostberg (Jernkont Ann 1960 144) (1) p. 46-76) showed that iron precipitated in grains of ilmenite by reduction occurred as discrete particles, the number of which per given volume was greater when hydrogen was used as the reductant than when carbon monoxide or solid carbon was used. The size of the particles was inversely proportional to the number. The number of particles could be increased by lowering the temperature used. These observations would indicate that to obtain a homogeneous dispersion of fine particles of metallic iron, hydrogen reduction should be used at the lowest practicable temperature. Unfortunately because of unfavourable reaction equilibria hydrogen reduction is considerably more costly to carry out than reduction with solid carbon.